(A)(1) Methane propellent in CBC’s possibly Methane/LH2 gel with a high mass fraction of Methane.

(A)(2) CBC Methane propellant tank high up on the vehicle , gravity feeds Methane to core stage LH2 tank that is placed at bottom of core stage.Would this cause mass shifting and balance issues in flight?

(A)(4) EELV heavy stands to gain the most from this concept as does a future SLS with Methane powered CBC’s.Imagine Vulcan with both Blue Origin Methane and LH2 core stage engines.A SpaceX commercial or Mars launch vehicle could benefit from a Methane core stage with Falcon 9 kerosene CBC’s? This concept would not be able to utilize cross feed however.